This disclosure generally relates to a fuel vapor processing apparatus that may be mounted to a vehicle.
A fuel vapor processing apparatus has been widely known that may be mounted to a vehicle, such as an automobile, for inhibiting fuel vapor from diffusion to the atmosphere. US Patent Application Publication No. 2009/0013973 (also published as Japanese Laid-Open Patent Publication No. 2009-19572) discloses a fuel vapor processing apparatus having three segmented adsorption chambers each containing an adsorbent. In this fuel vapor processing apparatus, one of the adsorbent chambers disposed adjacent to an atmospheric port may contain adsorbent granules having a relatively large diameter, while the other two adsorbent chambers disposed on the side of a purge port may contain adsorbent granules having a relatively small diameter. The adsorbent granules having the relatively large diameter may have a macro-porous structure to prohibit an increase in a resistance against flow of gas.
In general, release of fuel vapor to the atmosphere from a fuel vapor processing apparatus may occur if a vehicle is parked even a whole day. It may be considered that the external atmospheric air may serve as a heat source to cause fuel vapor to be released from the fuel vapor processing apparatus. The adsorption chamber containing the adsorbent granules having the relatively large diameter disclosed in the above noted Japanese Publication No. 2009-19572 may have a relatively large void ratio. Therefore, in the case of the fuel vapor processing apparatus disclosed in this publication, there is a possibility that fuel vapor desorbed from the adsorbent due to the heat of the external atmospheric air may flow through gaps between adjacent adsorption granules to leak to the outside via the atmospheric port.
In view of the challenges discussed above, there is a need for inhibiting fuel vapor from being discharged from an atmospheric port of a fuel vapor processing apparatus without causing an increase of a resistance against flow of gas through the fuel vapor processing apparatus.